Question: On the first 4 exams of his chemistry class, Luis got an average score of 82. What does he need on the next exam to have an overall average of 85?
Let his score on the next exam be $x$ The sum of all of his scores is then $4 \cdot 82 + x$ The same sum must also be equal to $5 \cdot 85$ Solve: $x = 5 \cdot 85 - 4 \cdot 82 = 97$.